The present invention relates to a magnetic disc device used in computers, information storage devices and so on, a magnetic storage device used in such information home appliances as digital VTRs, and a magnetic recording, and, more particularly, to a magnetic recording and reading device suitable for realizing high-speed recording and reading, and for high-density recording.
Semiconductor memories, magnetic memories, etc., are used in the storage or recording devices of information equipment. Semiconductor memories are used in internal primary storage in the light of high-speed accessibility and magnetic memories are used in external secondary storages in the light of a high capacity, low cost and nonvolatile property. Magnetic disk devices, magnetic tapes and magnetic cards are the main current in magnetic memories. A magnetic recording portion which produces a strong magnetic field is used in order for writing magnetic information in recording media, such as magnetic disks, magnetic tapes or magnetic cards. Further, reading portions based on the magnetoresistance effect or the electromagnetic induction effect are used in reading magnetic information recorded at a high density. In recent years, for reading, the giant magnetoresistance effect and the tunneling magnetoresistive effect have also begun to be examined. These functional portions for recording and reading are both installed in an input-output part which is called a magnetic head.
The basic configuration of a magnetic disk device is shown in FIGS. 10A and 10B. FIG. 10A shows a plan view of the device and FIG. 10B shows a vertical-sectional view of the device. Recording media 101-1 to 101-4 are fixed to a hub 104 to be rotated by a motor 100. In FIG. 10B shows one example which comprises four magnetic disks 101-1 to 101-4 and eight magnetic heads 102-1 to 102-8. However, the magnetic disk device may comprise at least one magnetic disk and at least one magnetic head. The magnetic heads 102-1 to 102-8 move on the rotating recording media. The magnetic heads 102-1 to 102-8 are supported by a rotary actuator 103 via arms 105-1 to 105-8. Suspensions 106-1 to 106-8 have function of the pressing the magnetic heads 102 against the recording media 101-1 to 101-4 under a determined load, respectively. A given electric circuit is needed for processing of reproduction signals and for inputting and outputting of information. Recently, a signal processing circuit in which waveform interference at high-density is positively utilized, such as PRML (Partial Response Maximum Likelihood) or EPRML (Extended PRML) which is an enhanced. PRML, has been adopted, contributing greatly to a high-density design. The signal processing circuit is installed in a circuit board on a cover 108, etc.
The functional portion for writing and reading information on a magnetic head assembly is comprises components shown in FIG. 11A, for example. A writing portion 111 is comprised of a spiral coil 116 between magnetic poles 117, 118 which are magnetically connected with each other. The magnetic poles 117, 118 are both composed of a magnetic film pattern, which are made of an NiFe alloy, etc., respectively. The reading portion 112 comprises a magnetoresistance element 113 made of an NiFe alloy, etc. and an electrode 119 for applying a constant current or a constant voltage to the element 113 and for detecting changes in resistance. The magnetic pole 118, which is made of an NiFe alloy, etc. and serves also as a magnetic shielding layer, is provided between the writing and reading portions. There is further a shielding layer 115 underneath the magnetoresistance element 113. A reading resolution is determined by the clearance distance between the shielding layer 115 and the magnetic pole 118 (serving also as another shielding layer). The functional portion is formed on a magnetic head slider 1110 (FIG. 11B) via an underlayer 114 made of Al2O3, etc. Incidentally, the magnetic head slider, which is provided with a protection layer made of hard-carbon, etc. on the surface opposed to the magnetic recording medium, is supported by a gimbal 1111 and a suspension 1113, as shown in FIG. 11B. The magnetic head slider moves relatively to the magnetic recording medium while floating from the medium surface and, after positioning in an arbitrary position by an arm 1114 connected to a motor, realizes the function of writing or reading magnetic information via lead lines 1116 and 1115. With respect to the above function, there is also provided an electric control circuit together with the aforementioned signal processing unit or on the head carriage.
A detailed structure of a recording medium is schematically shown in FIG. 12. As described in JP-A-3-16013, most of the conventionally used recording media are produced by forming a magnetic layer 123 made of a Co—Cr—Ta alloy, or a Co—Cr—Pt alloy, etc. on a non-magnetic substrate made of Al plated with an NiP alloy, a glass, a high-hardness ceramics, a polished Si or the like, or a plastic substrate 121 by the sputtering method, or the evaporation method, or the plating method, etc. Usually, an under layer 122 made of Cr, or a Cr alloy, etc. for orientation control of the magnetic layer is often formed on the substrate. Furthermore, a protection film 124 made of diamond-like carbon containing nitrogen and/or hydrogen, or SiO2 or SiN or ZrO2, etc. is provided to ensure durability of sliding resistance, and a lubricating film 125 made of perfluoroalkyl polyether having an adsorptive or a reactive end group, or organic fatty acids, etc. is provided.
In addition to the magnetic recording device, magneto-optic recording devices that perform recording and reading on a magnetic recording medium through the use of light have also been put to practical use. The magneto-optic recording devices are classified into one type in which recording is performed only by light modulation and another type in which recording and reproduction are performed by light with a modulated magnetic field. However, the both types greatly rely on heat when recording and reading. Therefore, according to such type of devices, it is impossible to perform recording and reading in high data transfer rate and thus they have been adopted mainly in backup systems, etc.
The importance of a storage device is determined by its storage capacity and the speed during inputting-outputting operations. In order to increase competitiveness of products, it is necessary for the storage device to increase capacity by higher recording density, higher rotational speed and higher data transfer rate than those of the prior art. Thus, an important problem to be solved by the present invention is to provide a device capable of recording and reading at a high data transfer rate of not less than 50 MB/s and, more preferably, that at a high density of not less than 5 Gb/in2. A magnetic recording medium capable of recording and reading at a high frequency and capable of obtaining a high S/N ratio at a high density and a magnetic head capable of generating a sufficient magnetic recording field at a high frequency are necessary for meeting the requirement.
In conventional magnetic recording media, there have been proposed and actually carried out to reduce noise by refining crystal grains in order to obtain a high S/N ratio at a high density of about 1 to 3 Gb/in2, and by promoting segregation of non-magnetic components at grain boundaries to reduce exchange coupling among crystal grains as being taught in JP-A-63-148411, JP-A-3-16013 and JP-A-63-234407 so as to make the coercive squareness S* to not more than 0.85 and the rotational hysteresis loss RH to the range of 0.4 to 1.3. Noise can be considerably reduced by recording and reading at a data transfer rate of not more than about 20 MB/s. However, when the magnetic recording was carried out on that film media of the prior art at a high frequency of not less than 50 MB/s, thermal fluctuation effects in fine magnetic crystallines is remarkable due to weak exchange coupling among crystal grains and the apparent coercive force is high resulting in that it was impossible to record on it accurately. Furthermore, even when recording is performed under a large current with utilization of a modified recording circuit, etc., the magnetic recording transition region is widened due to a broad magnetic recording field resulting in that noise increases and/or recorded information is lost when it was allowed to stand for a long time.